Temperature data for the first 11 months of 2002 indicate that this year will likely be the second warmest on record, exceeded only by 1998. These data from the Goddard Institute for Space Studies indicate that the temperature for the first 11 months has averaged 14.65 degrees Celsius (58.37 degrees Fahrenheit), down slightly from the record high of 14.69 in 1998, but well above the average temperature of 14 degrees Celsius that prevailed from 1951 to 1980.

Studying these annual temperature data, one gets the unmistakable feeling that temperature is rising and that the rise is gaining momentum. A year ago, we noted that the 15 warmest years since recordkeeping began in 1867 had occurred since 1980. Barring a dramatic drop in temperature for December, we can now say that the three warmest years on record have come in the last five years.

In addition to the longer-term annual temperature trend, recent monthly data also indicate an accelerating rise. In contrast to local temperatures, which fluctuate widely from season to season, the global average temperature is remarkably stable throughout the year because the seasonal contrasts of the northern and southern hemispheres offset each other. The temperature for January of this year of 14.72 degrees Celsius was the highest on record for January. The 14.91 degrees for March made it the warmest March on record. And in seven of the next eight months—April through November—the temperature was either the second or the third warmest. October was the fourth warmest.

Since 1980, decadal average temperatures have risen well above the 14 degrees Celsius average for the span from 1951 to 1980, which is defined as the norm. During the 1980s, the global temperature averaged 14.26 degrees. In the 1990s it was 14.38 degrees. During the first three years of this decade (2000-2002), it has been 14.52 degrees. (See data).

Rising temperature does not come as a surprise to atmospheric scientists who analyze the climate effects of rising atmospheric levels of carbon dioxide, the principal greenhouse gas. Each year since detailed recordkeeping began in 1959, the concentration of CO2 in the atmosphere has climbed to a new high, making it one of the most predictable of all global environmental trends.

The rise in atmospheric CO2 levels is the result of massive fossil fuel burning that has simply overwhelmed nature's capacity to absorb carbon dioxide. The temperature rises observed over the last two decades are in line with the results of research using computerized global climate models to project the effects of rising CO2 levels on the earth's climate.

The Intergovernmental Panel on Climate Change (IPCC), a group of more than 1,500 of the world's leading climate scientists, reports that if atmospheric CO2 levels continue to rise as projected, the earth's average temperature will rise by 1.4-5.8 degrees Celsius during this century. The lower end of the projected increases would lead to a 0.14 degree rise in temperature per decade during this century, roughly the same as during each of the last two decades of the last century. But the higher end of the projected temperature range means an increase of nearly 0.6 degrees per decade, a rate that could be extraordinarily disruptive to both the earth's ecosystem and the economy that depends upon it.

There are many manifestations of a higher temperature other than thermometer readings, including deadly heat waves, scorched crops, and ice melting. In May 2002, a record heat wave in southern India with the temperature reaching 114 degrees Fahrenheit (45.6 degrees C) claimed more than 1,000 lives in the state of Andhra Pradesh alone. In societies without air conditioning, there is no ready escape from the dangerous heat. To India's north, the temperatures in Islamabad, the capital of Pakistan, soared to 117 degrees Fahrenheit (47 degrees C) during June.

Farmers may now be facing higher temperatures than any generation of farmers since agriculture began 11,000 years ago. Crop yields have fallen as temperatures have climbed in key food-producing countries, such as the United States and India. Many weeks of record or near-record temperatures this past summer in the northern hemisphere, combined with low rainfall, withered crops in many countries, and reduced the 2002 world grain harvest to 1,813 million tons of grain, which was well below the projected consumption of 1,895 million tons.

Crop ecologists at the International Rice Research Institute in the Philippines have recently reported that rice fertilization falls from 100 percent at 34 degrees Celsius (93 degrees F) to essentially zero at 40 degrees (104 degrees F). Scientists in the U.S. Department of Agriculture are seeing a similar effect of high temperature on other grains. The scientific rule of thumb is that a 1 degree Celsius rise in temperature above the optimum reduces grain yields by 10 percent.

One of the most sensitive indicators of higher temperature is ice melting. Scientists now report ice melting in all the world's major mountain ranges, including the Rocky Mountains, the Andes, the Alps, and the Himalayas. In Alaska, where temperatures in some regions have risen 5-10 degrees Celsius over the norm, ice is melting far faster than had earlier been reported.

On Africa's snow-covered Kilimanjaro, the area covered by snow and ice has shrunk by 80 percent since 1900. Lonnie Thompson, Ohio State University glaciologist, reports that all the snow and ice there may disappear by 2020. For Americans, another landmark—Glacier National Park—may be forced to change its name. Half of its glaciers have already disappeared, and the U.S. Geological Survey projects that the remaining ones will disappear within the next 30 years.

Scientists report that ice cover in the Arctic Ocean shrank to 2 million square miles this summer compared with an average of 2.4 million square miles during the preceding 23 years. The thinning of the ice is proceeding even faster. Since this ice is already in the water, its loss will not affect sea level, but when incoming sunlight strikes snow and ice, 80 percent of it bounces back into space and 20 percent is converted to heat. Conversely, when the incoming sunlight hits open water, only 20 percent is reflected and 80 percent is converted into heat, warming the region.

Scientists are concerned with this warming because Greenland lies largely within the Arctic Sea. This past summer ice melting occurred over 265,000 square miles of the Greenland ice sheet—9 percent more than the previous maximum. If the Greenland ice sheet, which is 1.5 miles thick in some areas, were to melt entirely, sea level would rise 7 meters (23 feet). What happens to the ice in the Arctic Sea and the climate in the region is of concern to the entire world.

Some industries are beginning to respond. Worried about the loss of snow in mountainous regions and frustrated by the lack of progress in stabilizing climate, the National Ski Areas Association, the U.S. trade association for the industry, plans to soon announce its "Keep Winter Cool" campaign. To do its part to reduce carbon emissions, the industry plans to purchase wind-generated electricity to run lifts and snowmaking equipment. Other sectors of the economy, such as agriculture and the insurance industry, may also begin to press for a steep reduction in carbon emissions as the high costs of failing to stabilize climate become unacceptable.

Changing the earth's climate is a serious matter, one that should not be taken lightly. The risk is that climate change could soon spiral out of control, leaving future generations with soaring temperatures, withered harvests, deadly heat waves, melting ice, and rising seas. If we do not act quickly to stabilize climate, our grandchildren may never forgive us.

IPCC, Climate Change 2001. Contributions of Working Groups I, II, and II to the Third Assessment Report of the Intergovernmental Panel on Climate Change (Cambridge and New York: Cambridge University Press). Text and summaries available at http://www.ipcc.ch.